Make the vanilla dough by placing the butter, both sugars, salt and baking powder in the bowl of a standing mixer fitted with the paddle attachment. Cream the butter and sugar until it is light and fluffy, about three minutes on medium speed. Add the vanilla extract and split the vanilla bean lengthwise and scrape out the seeds into the batter with the back of a knife. Add the egg and beat to incorporate about 30 seconds.

Add the flour in three portions, beating to incorporate between additions, scraping down the sides with a large spatula. Once the flour is blended in, divide the dough in half and pat the dough down into a 6 inch square that is 1/2 inch thick. Wrap tightly with plastic wrap and refrigerate until firm 30 minutes to overnight. Repeat with the second half of the dough.

Make the chocolate dough by placing the butter, both sugars, and salt in the same bowl (don’t bother cleaning it) of the standing mixer fitted with the paddle attachment. Cream the butter and sugar until it is light and fluffy, about three minutes on medium. Add the chocolate and vanilla extracts and split the vanilla bean lengthwise and scrape out the seeds into the batter. Add the egg and beat to incorporate about 30 seconds.

Add the cocoa powder beating on slow speed to incorporate and scraping down the sides of the bowl with a large spatula. Add the flour in two portions, beating to incorporate between additions, scraping down the sides between additions. Once the flour is blended in, divide the dough in half and pat the dough down into a 6 inch square that is 1/2 inch thick. Wrap tightly with plastic wrap and refrigerate until firm 30 minutes to overnight. Repeat with the second half of the dough.

Pre heat the oven to 350 degrees Fahrenheit. Line two baking sheets with parchment paper or Silpat. Take the doughs out of the refrigerator. Brush the top of one of the vanilla squares with water. Place one of the chocolate dough squares on top of it, and press down firmly to adhere the dough. Brush the top of this chocolate dough with water and place the remaining vanilla dough square on top of that, pressing down firmly. Finally brush the top of this vanilla square with water and place the remaining chocolate dough on top of that, pressing down firmly. You should have a 2 inch thick stack of 6 x 6 square dough, alternating in layers. Wrap with plastic wrap and place back in the refrigerator until firm, about 30 minutes.

Once the dough has firmed up, trim the edges of the square to make a completely square piece of dough. Set the trimming aside for marbled zebra cookies as a bonus (instructions to follow). Cut a 1/2 inch strip from the square. Place one strip flat, and then brush it top of it with water. Cut another 1/2 inch strip from the square and rotate the strip 180 degrees so it alternates with the bottom strip. Place on the strip brushed with water and press firmly down. Repeat with the remaining cookie dough, chilling as needed if it warms up and becomes sticky.

To make marbled zebra cookies, brush the top of one trimming with water and place another trimming on top, alternating dough strips. Repeat until all the trimmings are placed on each other. Flatten and twist the trimmings together, turning clockwise with one hand, while counterclockwise with the other. Roll out the dough to a 12 inch length, and fold over once. Form the dough into a thick 1 1/2 inch roll pressing firmly down to make sure the different doughs stick together. Repeat with the remaining cookie dough, chilling the dough as needed if it warms up and becomes sticky. Slice each stack of dough into 1/2-inch thick cookies.

Place the cookies on the prepared baking sheets about 1 inch apart (keep the extra cookies chilled until ready to bake). Bake until the edges of the cookies start to brown ever so slightly, 12-14 minutes. Let cool on the baking sheet for 10 minutes and then move the cookies to a wire cooling rack to cool completely. Repeat with the remaining dough. Once you have finished baking the checkerboard cookies, remove the marbled log from the refrigerator and slice into 1/2 inch thick cookies. Bake for 12-14 minutes. Let cool on the baking sheets for 10 minutes before moving to a wire cooling rack to cool completely.